Luminescent zinc fluoride



Aug. 24, 1948.` F. E. WILLIAMS )2,447,927

LUMINESCENT ZINC FLUORIDE Filed oct. 17, 1945 Patented Aug. 24, 1948 UNITED LUMINESCENT ZINC FLUORIDE Ferd E. Williams, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 17, 1945, Serial No. 622,823

2 Claims. l

This invention relates to materials capable of fluorescing under excitation of agents, such as cathode rays, with a relatively long decay rate in luminescence when the excitation is removed.

In phosphore of the type disclosed, the intensity of luminescence is given by the equation I=At*", where A is a constant depending upon the particular ingredients and excitation intensity, t is time and n is a variable also dependent upon the ingredients of the mixture, particularly the activator used.

It is an object of this invention to provide a phosphor of good eicency and a relatively slow decay rate.

Another object is to provide a phosphor ci zinc fluoride with an activator capable of varying the decay rate.

Other objects of the invention will appear in the following specification, reference being had to the drawing, in which the single gure of the drawing contains graphs illustrating the performance of the improvement, the abscissas representing time in seconds in linear scale and the ordinates representing intensity of luminescence in logarithmic scale.

Zinc fiuoride with manganese activator has been found to be particularly efficient in radar and similar' uses because of its characteristic decay rate. The luminescence continues for a sufficient time to satisfactorily show the trace of moving objects and then blanks out suddenly. Such a phosphor is disclosed in the application of Maggio Banca, filed April 19, 1945, Serial No. 589,269.

I have found that zinc fluoride, when activated by columb-ium (also known as niobium), has a quitebroad spectrum with a peak at 4700 and that n in the equation ILAt-7L can be varied from 0.8 to 1.2 by increasing the columbium gram mole content from ZnF2:0.0008 Cby to ZnFz:0.03Cb. This control of the decay is an important ad- Vantage.

In the drawing, curve I shows the decay characteristic of the zinc fluoride phosphor when 0.0008 gram mole of columbium activator is used Number to each gram mole of Zinc fluoride. Curve 2 shows the ch-aracteristic with 0.03 gram mole of columbium per gram mole of zinc fluoride. It will be apparent that wide control of the decay rate can be obtained by varying the columbium content.

The phosphor may be prepared by adding C. P. concentrated hydroiluoric acid to zinc oxide and columbium of the desired content, either as a salt such as CbSO4x(OH)y, or as a metal. However, the use of metallic columbium, preferably in powder form, is preferred, as the sulphate or other anion decreases the efciency of the phosphor. The materials, after thorough mixing, are evaporated to dryness by heating for about onehalf hour at from 500 C. to 900 C. in a relatively neutral atmosphere.

The columbium activator is thought to exist in the iluorde crystal lattice as the oxide and not as the fluoride, since the latter boils at 229 C.

Having described my invention, what I claim 1s:

1. A phosphor consisting of zinc fluoride and an activator of columbium having a gram mole ratio to the zinc fluoride of substantially 0.0008 to 1.

2. A phosphor consisting of zinc fiuoride and columbium activator in the ratio of 0.0008 to 0.03 gram mole of columbium to one gram mole of zinc uoride.

FERD E. WILLIAMS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Name Date Fischer Aug. 4, 1936 McKeag Dec. 24 1940 CTI-IER REFERENCES Chem. Abstracts, vol. 18, page 2287. 

